This invention relates to apparatus for weighing a continuous stream of fluent material.
There is a method of weighing a continuous stream of fluent material which includes means to direct the material onto a weighing means which, in the direction of flow of the material, is arranged in a plane at an acute angle relative to a vertical plane and measuring, in a plane substantially parallel to the plane in which the weighing means is arranged, the load applied by the material to the weighing means and generating a signal representative of the mass of the material. To determine the mass flow, the velocity of the flow must be determined by a signal representative of the velocity. These two signals are then processed in an electronic device where also the total material weighed is calculated.
Most of the number of weighing apparatuses of this and similar types of practical reasons leave out the speed signal and the mass flow is to be determined by calibration with a known material flow. An example of equipment for producing a speed signal is disclosed in the U.S. Pat. No. 5,002,140, where a wheel with ribbed surface is placed where the material is leaving the weighing plate and can impinge to cause the wheel to rotate proportional to the speed of the material. Of reliability reasons the method is limited to suitable materials and the speed signal is not representing the mean value of the material sliding over the plate. It is also known from the European patent EP 0626062 (U.S. Pat. No. 5,495,773) to calculate the mean velocity from the changing of the flow profile when a particulate material is accelerating along the weighing plate. This is done by supporting the plate at two different levels along the tilted plate by force measuring means. A third force measuring means is also present to determine the friction force of the material against plate surface. The magnitude of the forces exerted relative the capacity of the bulk flow is relatively small, where the number of supporting and pivot points in combination with the small order of forces attacking the measuring means make the suggested constructions delicate. Especially where small differences between two measured forces are to be measured.
It is the object of the present invention to provide an apparatus of the kind referred to, which gives a simple and sturdy mechanical construction together with measuring of both the weight of the material and its velocity.
A continuous flow of fluid or particulate material sliding on a tilted plane increases its velocity by the gravitation force. The section of the stream thus decreases as the velocity increases. From this behavior the weight of the mass of the upper part will be larger than of the lower part. Around a horizontal axis straight across the centre part of the tilted plate a moment arises which is proportional to the difference of the masses on each side. It can be shown that the difference of the masses is proportional to the velocity of the material. By directly measuring that moment with a moment transducer one factor for determining the velocity of the mass flow will be given. The other factor is the sum of the weight of the material on the tilted plate. That is done with a load transducer, which just is measuring the load in the direction of or parallel to one specified axis, and placed below the moment transducer, it measures the total load on the plate regardless of its distribution over the surface of the tilted plate. The plate is attached in one central point on the underside of the plate or along a horizontal axis and the load transducer is attached to the ground carrying the plate via the moment transducer. It can be shown that the moment signal in combination with the weight signal will give a measurement of the flow. The background for the calculations is that the relative change in the height of the material sections in the upper and lower ends of the plate in comparison to the mean value of the height is proportional to the change of the velocity of the material flow in comparison with the mean velocity over the plate. Included in the invention is the calculating means for indicating the flow.